1. Field of the Invention
The present invention relates to a method of producing an electronic circuit and an electronic circuit.
2. Description of the Related Art
In producing a conventional electronic circuit board, a metal conductor pattern layer is formed on a metal thin film by performing resist application, exposure, development, etching and other processes. This manufacturing step requires an exposure mask for each layer, involving a great amount of time and cost for its design and production. Therefore, a change or modification in the circuit pattern has a large influence on the electronic circuit board production period and cost.
Accordingly, there is developed a method of forming a metal conductor layer without using an exposure mask by printing a base pattern having a desired pattern by electrophotography with charged particles containing fine metal particles in a resin used as toner, and performing electroless plating with the fine metal particles of the printed base pattern used as a plating nucleus (Japanese Patent Laid-Open Application No. Hei 7-263841).
The metal conductor layer needs a prescribed thickness according to a required electric resistance value. Generally, a thickness of 10 to 20 μm is required. Here, a metal deposition speed is about 1 to 2 μm/h in the electroless plating, and it takes five hours or more to form a metal conductor pattern having a thickness of 10 μm by electroless plating. Meanwhile, it takes about 10 minutes only to form a metal conductor layer having the same thickness by electrolytic plating because a metal deposition speed is about 1 μm/min in the electrolytic plating.
Thus, it is desired to form the metal conductor layer by electrolytic plating. Where the metal conductor layer is formed on the pattern by electrolytic plating, it is necessary to supply electric current to all patterns. However, because an ordinary pattern is used as an electric circuit, the overall circuit is mostly an assembly of electrically independent patterns. The electrolytic plating treatment can be performed by supplying electric current to the patterns on which electrolytic plating is deposited and which are mutually connected electrically by plating wires. However, an unnecessary plating wire must be removed after forming the metal conductor layer having a thickness of about 10 to 20 μm. When the pattern is formed of a single layer, the plating wires are drawn to the outer periphery of the circuit, and the circumferential portion may be cut finally. However, where the circuit board is multilayered, it is impossible to remove the plating wires only.